1. Field of the Invention
This invention concerns a method for defluorinating a perfluoroalkane to the corresponding more highly unsaturated fluorocarbon.
2. References
U.S. Pat. No. 3,192,274, issued to Baranauckas, et al., on June 29, 1965, discloses a process for removing non-terminal halogens from saturated perhalocarbons by heating the perhalocarbons over a carbon catalyst at a temperature between about 275.degree. and 450.degree. C. All of the disclosed perhalocarbons contain at least one chlorine atom.
Patrick, et al., Chemistry and Industry, 1557 and 1558 (1963), disclose that passage of certain perfluorodimethylcyclohexanes over unactivated granular carbon at 600.degree. C. gave a complex mixture of products including defluorinated products such as decafluoro-p- and -m-xylene. They also disclose defluorination of such compounds over iron and nickel. The authors state that perfuoro-1,2-dimethylcyclohexane is normally defluorinated by passage over iron gauze at 450.degree.-500.degree. to give decafluoro-o-xylene.
U.S. Pat. No. 2,709,182, issued to Farlow on May 24, 1955, discloses preparation of tetrafluoroethylene by a process wherein a fluorocarbon of at least three carbons and of a melting point no higher than 25.degree. C. is pyrolyzed by heating at a temperature of at least 1500.degree. C. Pyrolysis by passing the fluorocarbon between carbon electrodes is specifically disclosed.
U.S. Pat. No. 2,709,192, issued to Farlow on May 24, 1955, discloses a process for preparing tetrafluoroethylene wherein carbon tetrafluoride or hexafluoroethane or a mixture of these, is contacted with carbon at a temperature of at least 1700.degree. C. and the resultant reaction mixture is rapidly quenched.
U.S. Pat. No. Re. 23,425, issued to Harmon on Oct. 30, 1951, discloses a process for making completely halogenated polyfluorohydrocarbons comprising heating at a temperature of at least 125.degree. C. a completely halogenated ethylene of the formula CX.sub.2 .dbd.CX.sub.2, wherein X is halogen and at least 2 of the halogens are fluorine. The use of activated charcoal in the process is disclosed.
Bidinosti, et al., J. Am. Chem. Soc. 83, 3737-3743 (1961), disclose low pressure pyrolysis of chlorinated methanes and ethanes and of chlorofluoromethanes and chlorofluoroethanes over graphite to give, in some cases, dehalogenated products.
Baciocchi, in "The Chemistry of Halides, Pseudo-Halides and Azides", Patai and Rappoport editors, John Wiley & Sons, New York, 1983, Chapter 5, pages 161 to 201, has reviewed 1,2-dehalogenations and related reactions.